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Page - 22 MQ372-02
8.6.3. Starting and stopping I
2
C bus communications
SCL
START
condition
SDA
0.95
s ( Max. )
Repeated START(RESTART)
condition
STOP
condition
[ S ]
[ Sr ]
[ P ]
1) START condition, repeated START condition, and STOP condition
(1) START condition
•
The SDA level changes from high to low while SCL is at high level.
(2) STOP condition
• This condition regulates how communications on the I
2
C-BUS are terminated.
The SDA level changes from low to high while SCL is at high level.
(3) Repeated START condition (RESTART condition)
• In some cases, the START condition occurs between a previous START condition and the next
STOP condition, in which case the second START condition is distinguished as a RESTART
condition. Since the required status is the same as for the START condition, the SDA level changes
from high to low while SCL is at high level.
2) Caution points
∗1) The master device always controls the START, RESTART, and STOP conditions for communications.
∗2) The master device does not impose any restrictions on the timing by which STOP conditions affect
transmissions, so communications can be forcibly stopped at any time while in progress. (However,
this is only when this RTC module is in receiver mode (data reception mode = SDA released).
∗3) When communicating with this RTC module, the series of operations from transmitting the START
condition to transmitting the STOP condition should occur within 0.95 seconds. (A RESTART
condition may be sent between a START condition and STOP condition, but even in such cases the
series of operations from transmitting the START condition to transmitting the STOP condition should
still occur within 0.95 seconds.)
If this series of operations requires 0.95 seconds or longer, the I
2
C bus interface will be automatically
cleared and set to standby mode by this RTC module's bus timeout function. Note with caution that
both write and read operations are invalid for communications that occur during or after this auto
clearing operation. (When the read operation is invalid, all data that is read has a value of "1").
Restarting of communications begins with transfer of the START condition again
∗4) When communicating with this RTC module, wait at least 1.3 µs (see the tBUF rule) between
transferring a STOP condition (to stop communications) and transferring the next START condition (to
start the next round of communications).
SCL
SDA
61
µ
µµ
µ
s (Min.)
STOP
condition
START
condition
[ P ]
[ S ]